LONDON , England -LRB- CNN -RRB- -- In the developing world millions of people struggle to operate machinery , read from a blackboard , or just see the world around them , because they do n't have access to the eyeglasses they need .

Self-refraction glasses let the wearer adjust the lenses to suit their vision , without the need for an optometrist .

But a pair of glasses developed by Joshua Silver , a physics professor at the University of Oxford , offers an affordable solution .

The glasses can be adjusted to the right strength by the wearer without the need to visit an optometrist .

A major reason for that is a chronic shortage of optometrists -- in Ghana , for example , there is just one for every eight million people . That makes it incredibly difficult for ordinary people to visit an optometrist , without which it 's impossible for them to get glasses .

But Silver thinks he may have come up with a solution to the problem . His self-refraction glasses mean people can correct their vision without needing an optometrist -LRB- see Fact Box -RRB- .

`` Take a Sub-Saharan country where there is one optometrist for every million people ; those people will never see an optometrist , so how will they get eyewear ? , '' he told CNN .

`` Any model of delivery of vision correction in the developing world that depends on eye care professionals wo n't work . If you find a model that does n't rely on them , then you potentially have a solution . ''

Silver has been developing the glasses for over 20 years and continues to research the technology at the Center for Vision in the Developing World -LRB- CVDW -RRB- at the University of Oxford .

He told CNN that about 80 percent of those who try the glasses are able to correct their vision , but there are limitations . They ca n't be used to correct astigmatism and it 's not known if they are suitable for children , although the CVDW is currently running a study to determine if schoolchildren can correct their own vision with their teachers ' help .

So far , 30,000 pairs of self-refraction glasses have been distributed around the world , through an adult literacy program in Ghana and the U.S. Military Humanitarian and Civic Assistance -LRB- HCA -RRB- Program .

The man behind the HCA program was Kevin White . He has now retired from the military and has set up Global Vision 2020 to distribute self-adjustable glasses .

White has just returned from Liberia , where he trained 40 people from local NGOs to dispense the glasses . White sees charity organizations already working in developing countries as the key to distribution .

`` If I can train people from existing networks to dispense glasses , and they can spare one day each week or month to dispense the glasses , then they can see 50 to 100 people in a day -- and that 's a way to reach a lot of people , '' White told CNN .

But for the program to be sustainable , White says the next step is to train his dispensers to become trainers themselves , so that he builds a growing network of people in developing countries who can distribute the glasses .

Silver estimates that one billion people in the developing world do n't have access to the glasses they need , and he has said that he would like to see all of them wearing glasses by 2020 . But he is under no illusions that he can do it alone .

`` No one person or company can possibly deliver that many glasses by 2020 . There 's a big infrastructure that needs to be set up to do that , and I 'd like to see it happen , '' he told CNN .

Distribution is one problem , cost is another . Currently , it cost $ 19 to manufacture a pair of self-refraction glasses , and Silver acknowledges that the price needs to come down to a few dollars a pair to make them affordable .

Another issue is style . The glasses are currently functional , rather than fashionable , and that may limit their uptake , but more cosmetic versions are being developed .

Silver says far more research is needed before those one billion people get their glasses , but he sees his self-refraction technology as a step toward that goal .

He told CNN , `` It 's one of the world 's largest problems . There 's an immense amount of interest in solving it and self-refraction is one route that can assist with that . ''

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A lack of optometrists means many in the developing world ca n't get glasses

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Josh Silver has developed glasses with lenses that can be altered by the wearer

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The technology could be used to provide glasses for one billion people

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Global Vision 2020 is training charity workers to dispense the glasses